Handbook of Information Security Management
(Publisher: CRC Press LLC)
Author(s): Hal Tipton and Micki Krause, Consulting Editors
ISBN: 0849399475
Publication Date: 01/01/98

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Constraining I/O Operations

If desired, I/O instructions may be defined as privileged and issued only by the system control program after access authority has been verified. In this protection method, before the initiation of any I/O operations, a user’s program must notify the system control program of both the specific data and the type of process requested. The system control program then obtains information about the data set location, boundaries, and characteristics that it uses to confirm authorization to execute the I/O instruction.

The system control program controls the operation of user programs and isolates storage control blocks to protect them from access or alteration by an unauthorized program. Authorization mechanisms for programs using restricted system functions should not be confused with the mechanisms invoked when a general user requests a computing function. In fact, almost every system function (e.g., the user of any I/O device, including a display station or printer) implies the execution of some privileged system functions that do not require an authorized user.

Privilege Definition

All levels of system privileges must be defined to the operating system when hardware is installed, brought online, and made available to the user community. As the operating system is implemented, each user ID, along with an associated level of system privileges, is assigned to a predefined class within the operating system. Each class is associated with a maximum level of activity.

For example, operators are assigned to the class that has been assigned those functions that must be performed by operations personnel. Likewise, systems auditors are assigned to a class reserved for audit functions. Auditors should be permitted to perform only those tasks that both general users and auditors are authorized to perform, not those permitted for operators. By following this technique, the operating system may be partitioned to provide no more access than is absolutely necessary for each class of user.

Particular attention must be given to password management privileges. Some administrators must have the ability and therefore the authorization to change another user’s password, and this activity should always be properly logged. The display password feature, which permits all passwords to be seen by the password administrator, should be disabled or blocked. If not disabled, this feature can adversely affect accountability, because it allows some users to see other users’ passwords.

Privilege Control and Recertification

Privileged-entity access must be carefully controlled, because the user IDs associated with some system levels are very powerful and can be used inappropriately, causing damage to information stored within the computing resource. As with any other group of users, privileged users must be subject to periodic recertification to maintain the broad level of privileges that have been assigned to them. The basis for recertification should be substantiation of a continued need for the ID. Need, in this case, should be no greater than the regular, assigned duties of the support person and should never be allocated on the basis of organizational politics or backup.

A recertification process should be conducted on a regular basis, at least semi-annually, with the line management verifying each individual’s need to retain privileges. The agreement should be formalized yet not bureaucratic, perhaps accomplished by initialing and dating a list of those IDs that are to be recertified. By structuring the recertification process to include authorization by managers of personnel empowered with the privileges, a natural separation of duties occurs. This separation is extremely important to ensure adequate control. By separating duties, overallocation of system privileges is minimized.

For example, a system programmer cannot receive auditor privileges unless the manager believes this function is required within the duties of the particular job. On the other hand, if a special project requires a temporary change in system privileges, the manager can institute such a change for the term of the project. These privileges can then be canceled after the project has been completed.

Emergency Procedures

Privileged-entity access is often granted to more personnel than is necessary to ensure that theoretical emergency situations are covered. This should be avoided and another process employed during emergencies — for example, an automated process in which support personnel can actually assign themselves increased levels of privileges. In such instances, an audit record is produced, which calls attention to the fact that new privileges have been assigned. Management can then decide after the emergency whether it is appropriate to revoke the assignment. However, management must be notified so the support person’s subsequent actions can be tracked.

A much more basic emergency procedure might involve leaving a privileged ID password in a sealed envelope with the site security staff. When the password is needed, the employee must sign out the envelope, which establishes ownership of the expanded privileges and alerts management. Although this may be the least preferred method of control, it alerts management that someone has the ability to access powerful functions. Audit records can then be examined for details of what that ID has accessed. Although misuse of various privileged functions cannot be prevented with this technique, reasonable control can be accomplished without eliminating the ability to continue performing business functions in an efficient manner.

Activity Reporting

All activity connected with privileged IDs should be reported on logging audit records. These records should be reviewed periodically to ensure that privileged IDs are not being misused. Either a sample of the audit records should be reviewed using a predetermined methodology incorporating approved EDP auditing and review techniques or all accesses should be reviewed using expert system applications. Transactions that deviate from those normally conducted should be examined and, if necessary, fully investigated.

Under no circumstances should management skip the regular review of these activities. Many organizations have found that a regular review process deters curiosity and even mischief within the site and often produces the first evidence of attempted hacking by outsiders.

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